Fuel injector provided with provided with a pressure transmitter controlled by a servo valve

ABSTRACT

A fuel injector for injecting fuel into a combustion chamber of an internal combustion engine, including a pressure booster, whose booster piston separates a work chamber, subjected to fuel via a pressure reservoir, from a pressure-relievable differential pressure chamber. A pressure change in the differential pressure chamber is effected via an actuation of a servo valve, which opens or closes a hydraulic connection of the differential pressure chamber to a first low-pressure-side return. The servo valve has a piston guided between a control chamber and a first hydraulic chamber. On this servo valve piston, a hydraulic face that positions the servo valve piston constantly in the opening direction when system pressure is applied and a first sealing seat that closes or opens a low-pressure-side return are embodied.

FIELD OF THE INVENTION

For introducing fuel into direct-injection internal combustion engines,stroke-controlled injection systems with a high-pressure reservoir(common rail) are used. The advantage of these injection systems is thatthe injection pressure can be adapted over wide ranges to the load andrpm. To reduce emissions and to attain high specific output, a highinjection pressure is necessary. The attainable pressure level ofhigh-pressure fuel pumps is limited for reasons of strength, so that tofurther increase the pressure in fuel injection systems, pressureboosters are used in the fuel injectors.

BACKGROUND OF THE INVENTION

German Patent Disclosure DE 101 23 913 has a fuel injection system forinternal combustion engines, with a fuel injector that can be suppliedfrom a high-pressure fuel source, as its subject. Connected between thefuel injector and the high-pressure fuel source is a pressure boosterdevice that has a movable pressure booster piston. The pressure boosterpiston divides a chamber that can be connected to the high-pressure fuelsource from a high-pressure chamber that communicates with the fuelinjector. By filling a differential pressure chamber of the pressurebooster device with fuel, or evacuating the differential pressurechamber of fuel, the fuel pressure in the high-pressure chamber can bevaried. The fuel injector has a movable closing piston for opening andclosing injection openings. The closing piston protrudes into a closingpressure chamber, so that the closing piston can be subjected to fuelpressure to attain-a force acting in the closing direction on theclosing piston. The closing pressure chamber and the differentialpressure chamber are formed by a common closing pressure differentialpressure chamber; all the subsidiary regions in the closing pressuredifferential pressure chamber communicate with one another permanentlyfor exchanging fuel. A pressure chamber is provided for supplying theinjection openings with fuel and subjecting the closing piston to aforce acting in the opening direction. A high-pressure chambercommunicates with the high-pressure fuel source in such a way that inthe high-pressure chamber, aside from pressure fluctuations, at leastthe fuel pressure of the high-pressure fuel source can always beapplied; the pressure chamber and the high-pressure chamber are formedby a common injection chamber. All the subsidiary regions of theinjection chamber communicate permanently with one another forexchanging fuel.

German Patent Disclosure DE 102 294 15.1 relates to a device for needlestroke damping in pressure-controlled fuel injectors. A device forinjecting fuel into a combustion chamber of an internal combustionengine is disclosed that includes a fuel injector which can be subjectedto fuel that is at high pressure via a high-pressure source. The fuelinjector is actuated via a metering valve, and an injection valve memberis surrounded by a pressure chamber, and the injection valve member canbe urged in the closing direction by a closing force. The injectionvalve member is assigned a damping element, which is movableindependently of it and which defines a damping chamber and has at leastone overflow conduit for connecting the damping chamber to a furtherhydraulic chamber. In DE 102 294 15.1, the control of the fuel injectoris effected with a 3/2-way valve, and as a result, although an injectorthat is economical in both cost and installation space can be defined,nevertheless this valve must control a relatively large return quantityof the pressure booster.

Instead of the embodiment of a 3/2-way valve known from DE 102 294 15.1,servo valves may also be used, which in the state of repose of the servovalve are embodied in nonleaking fashion on the guide portion, which isfavorable to the efficiency of a fuel injector. A disadvantage, however,is the fact that in the opened state of the servo valve piston of the3/2-way valve, no pressure face pointing in the opening direction of thepiston is subjected to system pressure. As a result, the movement of theservo valve piston in its housing is quite vulnerable to productiontolerances. Moreover, a slow opening speed of the servo valve pistoncannot be attained, and thus the minimum-quantity capacity of a servovalve configured in this way is limited. In the opened state of theservo valve piston, only an inadequate closing force ensues at a secondvalve seat embodied on it, and the result can be leaks and increasedwear.

SUMMARY OF THE INVENTION

To attain a defined motion of a piston of a servo valve for actuating afuel injector, a servo valve embodied as a 3/2-way valve is proposed,which has a hydraulically operative face that can be urged in theopening direction and that is constantly subjected to system pressure.The system pressure is equivalent to the pressure level prevailing inthe high-pressure reservoir. By this provision, the motion of the servovalve piston can be adjusted without problems by adapting an inlet andoutlet throttle on the servo valve. By means of a slowly proceedingopening motion of the servo valve piston, good definition of smallpreinjection quantities and a nonfluctuating pressure buildup can beassured. Because of the defined opening force, the servo valve proposedaccording to the invention is not vulnerable to tolerances in terms ofthe effects of friction, so that a production-dictated deviation intolerances, with attendant major deviations in injection quantities, canbe avoided.

The servo valve proposed according to the invention, embodied as a3/2-way valve, moreover, in its state of repose, has no leakage flowsthat occur at a guide portion. This means a considerable improvement inthe injector efficiency; because of the small guide lengths thuspossible on the servo valve piston, a short structural length of theservo valve can be made possible, which favorably affects the totalstructural height of a fuel injector with a pressure booster in aninjector body, including the servo valve; that is, the space needed forthis kind of fuel injector is reduced considerably.

If a sealing seat, embodied on the servo valve piston of the servovalve, is embodied as a flat seat, then advantageously the housing ofthe servo valve can be embodied as a multi-part housing, making itpossible to compensate for an axial offset of components from oneanother. This capability of compensating for production-dictatedcomponent tolerances and the ease of manufacture of the sealing seatassure simple, inexpensive production of the servo valve proposedaccording to the invention.

DRAWING

The invention will be described in further detail below in conjunctionwith the drawing:

Shown are:

FIG. 1, a first variant embodiment of a servo valve, embodied as a3/2-way valve, with a servo valve piston free of guidance leakage;

FIG. 2, a further variant embodiment of a servo valve piston of a3/2-way servo valve with a first seat embodied as a conical sealing seatand a further seat embodied as a slide seal;

FIG. 3, a variant embodiment of a 3/2-way servo valve with a servo valvepiston on which a control sleeve is received; and

FIG. 4, a variant embodiment of a 3/2-way servo valve with an elongatedservo valve piston.

VARIANT EMBODIMENTS

In FIG. 1, a first variant embodiment of a 3/2-way servo valve proposedaccording to the invention, for triggering a fuel injector that containsa pressure booster, can be seen.

Via a pressure source 1 and a high-pressure supply line 2 connected toit, a work chamber 5 of a pressure booster 3 is subjected to fuel thatis at high pressure. The work chamber 5 is subjected permanently to thefuel, at high pressure, of the pressure source 1. The pressure booster 3includes a one-piece booster piston 4, which separates the work chamber5 from a differential pressure chamber 6. The booster piston 4 issubjected to a restoring spring 8, which is braced on one end on asupport disk 7 and on the other on a stop disk mounted on a protrusionof the booster piston 4. The pressure booster 3 moreover includes acompression chamber 9, which communicates via an overflow line 10 with acontrol chamber 12 for an injection valve member 14. A first throttlerestriction 11 is received in the overflow line 10 from the differentialpressure chamber 6 to the control chamber 12 for the injection valvemember 14.

A spring element 13 is received in the control chamber 12 for theinjection valve member 14 and acts upon one face end of the needle-likeinjection valve member 14. The injection valve member 14 includes apressure step, which is surrounded by a pressure chamber 16. Thepressure chamber 16 is subjected to fuel that is at boosted pressure viaa pressure chamber inlet 17 that branches off from the compressionchamber 9 of the pressure booster 3. From the differential pressurechamber 6 of the pressure booster 3, a diversion line 21 extends intothe first housing part 26 of the servo valve housing 25. The end face ofthe booster piston that acts upon the compression chamber 9 of thepressure booster 3 is identified by reference numeral 20. Because of thepressure step at the injection valve member 14, the injection valvemember executes an opening motion when the pressure chamber 16 is actedupon by pressure, so that from the pressure chamber 16, fuel flows toinjection openings 22 along an annular gap and reaches a combustionchamber 23 of a self-igniting internal combustion engine.

The control chamber 12 that acts on the injection valve member 14communicates hydraulically with the compression chamber 9 of thepressure booster 3 via a second throttle restriction 15.

Above the injector body 19 of a fuel injector 18, there is a servo valvehousing 25, which receives a servo valve 24. In the variant embodimentshown in FIG. 1, the servo valve housing 25 is embodied in two parts andincludes a first housing part 26 and a second housing part 27. Thetwo-part embodiment of the servo valve housing 25 in the shown in FIG. 1allows good accessibility for machining the sealing seat and a slideedge, making the servo valve 24 simple and economical to produce.

From the high-pressure supply line 2, by way of which the work chamber 5of the pressure booster 3 is subjected to fuel that is at high pressure,a supply line 29 branches off into the valve housing 25. The supply line29 discharges into a first hydraulic chamber 38 of the first housingpart 26 of the servo valve housing 25. The first hydraulic chamber 38surrounds a servo valve piston 32, which includes a through conduit 33.A third throttle restriction 34 is embodied in the through conduit 33 ofthe servo valve piston 32. Via the through conduit 33, fuel flows fromthe first hydraulic chamber 38 into a control chamber 36 of the servovalve 24. A pressure relief of the control chamber 36 is effected uponactuation of a switching valve 30, upon whose opening, control volumefrom the control chamber 36, via a return that contains an outletthrottle restriction 37 (fourth throttle restriction), communicates witha further low-pressure-side return 31, and fuel can be diverted intothis return. The control chamber 36 of the servo valve 24 is defined byan end face 35 on the top side of the servo valve piston 32. Thiscontrol chamber is located at the head of the servo valve piston 32,opposite an annular face which is operative in the opening direction ofthe servo valve piston 32 and is acted upon by the pressure prevailingin the first hydraulic chamber 38. Also embodied on the servo valvepiston 32 are a first sealing seat 40, in a second hydraulic chamber 39,and a control edge 41. Via the first sealing seat 40, the communicationwith an outlet control chamber 42, from which a low-pressure-side return28 branches off, is opened and closed. By means of the control edge 41,which in the variant embodiment shown in FIG. 1 for the servo valve 24is embodied as a slide sealing edge 43, the first hydraulic chamber 38,which is at system pressure, is sealed off from the second hydraulicchamber 39 while the servo valve piston 32 is moving in the verticaldirection. The two returns 28, 31 on the low-pressure side are if at allpossible combined into one return, which discharges into a fuel tank.

To reinforce the motion of the servo valve piston 32 in the firsthousing part 26, spring forces—although not shown in FIG. 1—can bebrought to bear on the servo valve piston 32 via springs. A firstvariant embodiment of the servo valve 24 shown in FIG. 1 makes anextremely compact construction of the servo valve 24 possible. In theview in FIG. 1, the first sealing seat 40 of the servo valve 24 isembodied as a flat seat, but it could also be embodied as a conical seat(as shown in FIG. 2), a ball seat, or a slide edge. Advantageously,embodying the first sealing seat 40 as a flat seat makes it possible touse a valve body 25 constructed in multiple parts. By means of the firstsealing seat 40 embodied as a flat seat, any axial offsets that mightoccur as a result of production variations can be compensated forwithout problems. Moreover, by means of the closing force on the flatseat of the first sealing seat 40, brought to bear in the controlchamber 36 of the servo valve 24, a very high pressure per unit ofsurface area and hence good sealing are attained. The first sealing seat40 may be embodied as either a sealing edge or a sealing face. Thesealing force can be adjusted via the pressure face opposite the outletcontrol chamber 42. As a result, when a sealing face is used, optimaldesign of the pressure per unit of surface area is possible, as a resultof which both adequate tightness on the one hand and only slight wear onthe other can be achieved.

FIG. 2 shows a further variant embodiment of the servo valve proposedaccording to the invention, in which its first sealing seat is embodiedas a conical sealing seat.

The view in FIG. 2 also shows a fuel injector 18 which contains apressure booster 3. The work chamber 5 of the pressure booster 3 issupplied with fuel that is at high pressure via a pressure source 1(common rail) via the high-pressure supply line 2. In a distinction fromthe embodiment of the pressure booster 3 in the variant embodiment ofFIG. 1, the booster piston 4 of the pressure booster 3 as shown in FIG.2 is embodied in multiple parts. A support disk 7 is let into theinjector body 19 of the fuel injector 18 and represents an upper stopface for the upper part of the multi-part booster piston 4. The lowerpart of the booster piston 4 is acted upon by a restoring spring 8 thatis braced on the housing; the compression chamber 9 of the pressurebooster 3 is defined by way of the end face 20 of the lower part of thebooster piston 4. From the differential pressure chamber 6 of thepressure booster 3, an overflow line 10 which contains the firstthrottle restriction 11 branches off. The overflow line 10 connects thedifferential pressure chamber 6 of the pressure booster 3 to the controlchamber 12 for controlling the reciprocating motion of the injectionvalve member 14, which is embodied in the form of a needle. The pressurechamber inlet 17 extends from the compression chamber 9 of the pressurebooster 3 and discharges into the pressure chamber 16 surrounding theinjection valve member 14. The injection valve member 14 includes apressure step, which has a hydraulically operative face. The latter isengaged by the fuel pressure prevailing in the pressure chamber 16,which opens the injection valve member 14, so that fuel is injected viainjection openings 22, which discharge into the combustion chamber ofthe self-igniting internal combustion engine and which are opened uponopening of the injection valve member 14.

In a distinction from the variant embodiment shown in FIG. 1, a dampingpiston 51 is received in the control chamber 12 for the injection valvemember 14. The damping piston 51 is penetrated by a vertically extendingconduit 53. The conduit 53 communicates hydraulically with the controlchamber 12, via a fifth throttle restriction 52 in the wall of thedamping piston 51. An annular face 55 embodied on the damping piston 51is acted upon by a spring element 54 braced on the housing. From thecontrol chamber 12 for the injection valve member 14, a filling line 56,which contains a refill valve 50 that may be embodied as a check valve,extends to the compression chamber 9 of the pressure booster 3. Via thefilling line 56 that contains the refill valve 50, the compressionchamber 9 of the pressure booster 3 is refilled with fuel.

In the variant embodiment shown in FIG. 2, the servo valve 24 isreceived in the valve body 25. The servo valve 24 includes the controlchamber 36, which can be pressure-relieved into the secondlow-pressure-side return 31 via the switching valve 30. An outletthrottle 37 (fourth throttle restriction) is received between thecontrol chamber 36 and the switching valve 30. Diametrically oppositethe control chamber 36 in the valve body 25 of the servo valve 24 is thefirst hydraulic chamber 38, which is separated by the control edge 41from the second hydraulic chamber 39, in this case configured conically.The second hydraulic chamber 39 communicates with the differentialpressure chamber 6 of the pressure booster 3. In the variant embodimentof the servo valve 24 in FIG. 2 as well, the control edge 41 is embodiedas a slide sealing edge 43. Unlike the variant embodiment of the servovalve 24 shown in FIG. 1, the first sealing seat 40 of the servo valvepiston 32 is embodied as a conical seat. When the first sealing seat 40is closed, the outlet control chamber 42 embodied in the valve body 25below the servo valve piston 32 is sealed off, so that the firstlow-pressure-side return 28 is closed.

In a modification of the servo valve piston 32 as shown in FIG. 1, thecontrol chamber 36 and the first hydraulic chamber 38 are subjected topressure in parallel via the supply line 29, which branches off from thework chamber 5 of the pressure booster 3. Thus via the supply line 29,system pressure prevails both in the first hydraulic chamber 38, whichis acted upon via the second supply line portion 58, and in the controlchamber 36 of the servo valve 24, via a first supply line portion 57that includes the third throttle restriction 34. Because of the identityof the pressures in the first hydraulic chamber 38 and the controlchamber 36, a guidance leakage along the head of the servo valve piston32 is precluded. The servo valve piston 32 is guided inhigh-pressure-proof fashion in the valve body 25. In the position ofrepose, system pressure prevails inside the guide region of the head ofthe servo valve piston 32 on both sides, that is, in both the controlchamber 36 and the first hydraulic chamber 38, so that no leakage flowto the low-pressure side occurs. The entire region of the servo piston32, that is, the control chamber 36, the first hydraulic chamber 38, andthe second hydraulic chamber 39 along with the control edge 41, issealed off in a manner free of guidance leakage from the outlet controlchamber 42, via the first sealing seat 40 embodied in the secondhydraulic chamber 39, and thus also from the first low-pressure-sidereturn 28.

The basic mode of operation of the fuel injector proposed according tothe invention, which is triggered via the servo valve 24, will now bedescribed in conjunction with FIG. 1.

The work chamber 5 of the pressure booster 3 communicates constantlywith the pressure source 1 and is constantly at the pressure levelprevailing there. The compression chamber 9 of the pressure booster 3communicates constantly via the pressure chamber inlet 17 with thepressure chamber 16, which surrounds the injection valve member 14.Furthermore, the pressure booster 3 includes the differential pressurechamber 6 which to control the pressure booster 3 is either acted uponby system pressure, which is the pressure level prevailing in thepressure source 1, or pressure-relieved into the low-pressure-sidereturn 28 by being disconnected from the system pressure. In thedeactivated state, the differential pressure chamber 6 of the pressurebooster 3 communicates with the pressure reservoir 1, via the diversionline 21, the opened control edge 41, and the supply line 29, so that thepressures in the work chamber 5 and in the differential pressure chamber6 of the pressure booster are equivalent to one another, and the boosterpiston 4 is in equilibrium, and no pressure boosting occurs.

To activate the pressure booster 3, a pressure relief of thedifferential pressure chamber 6 is effected. To bring about thispressure relief, the switching valve 30 is activated, that is, opened,and the control chamber 36 of the servo valve 24 is relieved into thelow-pressure-side return 31, via the outlet throttle restriction 37.Because of the dropping pressure in the control chamber 36, the servovalve piston 32 moves vertically upward, being moved by the pressureforce engaging the opening face 44 in the first hydraulic chamber 38. Asa result, the first sealing seat 40 is opened, while the control edge 41is closed, since the slide edge 43 covers the housing edge diametricallyopposite it of the valve body 25. Because of the design of the throttlerestriction 34 in the through conduit 33 of the servo valve piston 32and because of the outlet throttle 37, the speed of motion of the servovalve piston 32 in its opening motion can be adjusted arbitrarily.Because of the defined opening face 44 on the underside of the head ofthe servo valve 24, a pressure force that urges the servo valve piston32 in the opening direction constantly prevails there. As a result, anexact motion of the servo valve piston 32 and hence its stably remainingat the opening stop in the open state of the servo valve piston 32 canbe brought about.

When the servo valve piston 32 is in its opening position, a decouplingof the differential pressure chamber 6 of the pressure booster 3 fromthe system pressure, that is, the pressure level prevailing in thepressure reservoir 1, takes place. With the control edge 41 closed, anoutflow of a control quantity takes place from the differential pressurechamber 6 via the diversion line 21 into the second hydraulic chamber 39and via the open first sealing seat 40 into the outlet control chamber42. From there, the fuel quantity diverted from the differentialpressure chamber 6 flows into the low-pressure-side return 28.

Because of the inward motion of the end face 20 of the booster piston 4into the compression chamber 9, a pressure increase takes place in thatchamber, so that via the pressure chamber inlet 17, fuel at increasedpressure, in accordance with the boosting ratio of the pressure booster3, flows to the pressure chamber 16 that surrounds the injection valvemember 14. Because of the pressure step embodied on the injection valvemember 14 in the region of the pressure chamber 16, the injection valvemember opens counter to the action of the spring 13, and as a result theinjection nozzles 22 on the end of the fuel injector 18 toward thecombustion chamber are opened, and fuel can be injected into thecombustion chamber 23 of the engine. When the injection valve member 14is fully opened, the second throttle restriction 15 between the controlchamber 12 and the compression chamber 9 of the pressure booster 3 isclosed, so that no loss flow occurs during the injection event.

To terminate the injection event, another actuation of the switchingvalve takes place, moving it into its closing position, so that in thecontrol chamber 36, the system pressure prevailing in the pressurereservoir 1 builds up, via the through conduit 33, the first hydraulicchamber 38, and the supply line 29 discharging into this hydraulicchamber. Because of the pressure force building up in the controlchamber 36, the servo valve piston 32 moves downward into its outsetposition, whereupon the first sealing seat 40 is closed toward thelow-pressure-side return 28 and the control edge 41 is opened. Since theend face 35, upon which the pressure prevailing in the control chamber36 acts, is dimensioned as larger than the opening pressure face 44 inthe first hydraulic chamber 38, a defined and rapidly proceeding closingmotion of the servo valve piston 32 into its closing position isachieved.

To reinforce the reciprocating motion of the servo valve piston 32,additional springs may also be located in the first housing part 26.

In the differential pressure chamber 6 of the pressure booster and inthe control chamber 12, by way of which the injection valve member 14 iscontrolled, a pressure buildup now takes place, to the pressure levelprevailing in the pressure reservoir 1, via the supply line 29, whichbranches off from the high-pressure supply line 2 of the high-pressurereservoir 1, the opened control edge 41, the second hydraulic chamber39, and the diversion line 21, which discharges into the differentialpressure chamber 6. From there, a pressure buildup takes place via theoverflow line 10, which contains the first throttle restriction 11, intothe control chamber 12.

Simultaneously, upon the pressure buildup in the differential pressurechamber 6 of the pressure booster, refilling of the compression chamber9 takes place, via the line, in which the second throttle restriction 15is embodied, that branches off from the control chamber 12 for actuatingthe injection valve member 14.

The first sealing seat 40 may be embodied as a flat seat, which makes ahigh pressure per unit of surface area possible, or a conical seat (asshown in FIG. 2), as a ball seat, or as a slide edge. Via the flat seatshown in FIG. 1 as the first sealing seat 40, any axial offset that mayoccur for production reasons can be compensated for. By way of the highpressure level prevailing in the control chamber 36, the generation of asufficient closing force is accomplished, so that a pressure per unit ofsurface area occurs at the first sealing seat 40 in its closingposition, and good sealing action thus remains assured.

With the variant embodiment shown in FIG. 2, using a damping piston 51which acts upon the injection valve member 14, a reduction in theopening speed of the needle-like injection valve member 14 can beattained. The damping behavior of the damping piston 51 can be adjustedby way of the dimensioning of the spring element 54 acting upon it andthe dimensioning of the throttle element 52 embodied in the wall of thedamping piston 51. In the variant embodiment shown in FIG. 2, therefilling of the compression chamber 9 of the pressure booster 3 iseffected not via the second throttle restriction 15 as in the variantembodiment of FIG. 1, but rather via a filling line 56, branching offfrom the control chamber 12 of the injection valve member 14, in whichline a refill valve 50 embodied as a check valve is received.

The 3/2-way servo valve 24 proposed by the invention may be employed tocontrol all the pressure boosters 3 that are triggered via a pressurechange of their differential pressure chamber 6.

From FIG. 3, a variant embodiment can be seen of a 3/2-way servo valvehaving a servo valve piston on which a control sleeve is received.

The variant embodiment shown in FIG. 3 of a fuel injector 18 with apressure booster 3 is supplied with fuel, which is at high pressure, viaa high-pressure source 1 via the high-pressure supply line 2. The workchamber 5 of the pressure booster 3 is filled with system pressure viathe high-pressure supply line 2, and received in the work chamber is arestoring spring 8, which is braced on one side on a support disk 7 andon the other side is prestressed via a stop face of the booster piston 4that separates the work chamber 5 from the differential pressure chamber6. The face end 20 of the booster piston 4 defines the compressionchamber 9, from which, upon activation of the pressure booster 3, thepressure chamber 16 is filled with fuel that is at high pressure, viathe pressure chamber inlet 17.

The variant embodiment of the fuel injector 18 shown in FIG. 3 includesthe control chamber 12, which is defined by a control chamber sleeve 62.The control chamber sleeve 62 is prestressed via the spring 13, and thespring 13 is braced on a collar of the injection valve member 14. Inflowfaces 64 are embodied on the injection valve member 14, below thecollar, in the form of polished sections. Via these inflow faces 64, thefuel flows from the pressure chamber to injection openings 22, whichdischarge into the combustion chamber of the self-igniting engine. Thecontrol chamber 12 of the fuel injector 18 is subjected to fuel on oneside via a first throttle restriction 11, which branches off from thepressure chamber inlet 17; the pressure relief of the control chamber 12is effected via the second throttle restriction 15, upon actuation of aswitching valve 60. If the switching valve 60 is actuated, then adiversion quantity is diverted into an injector return 61 via the secondthrottle restriction 15.

The pressure booster 3 in the variant embodiment shown in FIG. 3 isactuated via the servo valve 24. The servo valve 24 includes the valvepiston 32, which has a servo valve piston portion 65. The servo valvepiston 32, 65 is controlled via the subjection of the control chamber 36to pressure or the pressure relief thereof. On the compression side, thecontrol chamber 36 of the servo valve 24 is subjected to fuel that is athigh pressure via the first supply line portion 57, in which thethrottle restriction 34 is received. A pressure relief of the controlchamber 36 of the servo valve 24 is effected via an actuation of theswitching valve 30. Upon its actuation, a diversion volume flows out ofthe pressure-relieved control chamber 36 of the servo valve 24, via theoutlet throttle 37 (fourth throttle restriction) into the return 31provided on the low-pressure side.

The servo valve 24 includes a housing 25 that includes a plurality ofhousing parts 26, 27.

The servo valve piston 32, 65 is surrounded by both the first hydraulicchamber 38 and the second hydraulic chamber 39. The first hydraulicchamber 38 is acted upon by fuel that is at high pressure via the supplyline 29 that branches off from the high-pressure supply line 2. Thediversion line 21, by way of which a pressure relief of the differentialpressure chamber 6 of the pressure booster 3 is effected, dischargesinto the second hydraulic chamber 39.

The servo valve piston 32 furthermore includes the hydraulic face 44,which is engaged, upon pressure relief of the control chamber 36 of theservo valve 24, by a pressure force that moves the servo valve piston 32in the opening direction. First recesses 63, which have slide sealingedges 43, are embodied in the servo valve piston portion 65. The slidesealing edges 43 of the first recesses 63 cooperate with a control edge41 embodied on the second housing part 27. A control sleeve 67 isreceived on the servo valve piston portion 65 and is prestressed by acontrol sleeve spring 68, which is braced in turn on the first housingpart 26 of the servo valve housing 25. The control sleeve 67 has arecess 71. The first sealing seat 40, in the variant embodiment shown inFIG. 3, is designed as a flat seat and seals off the diversion chamber42 (low-pressure chamber) from the low-pressure-side return 28. The modeof operation of the variant embodiment shown in FIG. 3 of the fuelinjector 18 with a pressure booster 3, triggered via the servo valve 24,is as follows:

In the outset state, system pressure prevails in the control chamber 36of the servo valve 24; this pressure prevails in the control chamber 36via the third throttle restriction 34 when the switching valve 30 isclosed. As a result of the pressure force inside the control chamber 36of the servo valve piston, which acts on the end face 35 of the servovalve piston 32 and is higher than the opening pressure force that isapplied via the face 44 on the servo valve piston 32 that ishydraulically operative in the opening direction, the servo valve piston32 is moved into its lower position. In this position, the control edge41 and the slide sealing edge 43 at the servo valve piston portion 65are open, while conversely the slide seal 69 at the servo valve pistonportion 65 is closed. Moreover, the first sealing seat 40 toward thediversion chamber 42 (low-pressure chamber) is in its closed position.Since the second hydraulic chamber 39 is sealed off from the diversionchamber 42 (low-pressure chamber) by the first sealing seat 40, noleakage flow into the low-pressure-side return 28 occurs when the servovalve piston 32, 65 is closed, and as a result, less stringent demandscan be made in terms of the guidance leakage (guide length and play) ofthe control sleeve 67 received on the servo valve piston portion 65.

The first sealing seat 40 may be designed in manifold ways. Besides theembodiment of the first sealing seat 40 as a flat seat as shown in FIG.3, it may also be embodied as a conical seat, as in the variantembodiment shown in FIG. 2, or as a ball seat. The embodiment of thefirst sealing seat 40 as a flat seat in conjunction with a multi-partservo valve housing 25 as shown in FIG. 3 is especially advantageous. Bymeans of a multi-part valve body, such as the housing parts 26, 27 andincluding 66, simple manufacture of the valve seat of the first sealingseat 40 can be achieved. As a result of the flat seat shown in FIG. 3,any axial offset of the valve bodies relative to one another that mayoccur is compensated for. The variant embodiment shown in FIG. 3furthermore has a strong closing pressure force, exerted by the fuelpressure, prevailing in the control chamber 36, against the firstsealing seat 40, and as a result, high pressure per unit of surface areaand hence excellent sealing action are established at this sealing seat.

In the state of the repose of the servo valve 24, the differentialpressure chamber 6 of the pressure booster 3 is subjected to systempressure via the first recesses 63 on the servo valve piston 65 and thepressure booster 3 remains in communication with the differentialpressure chamber because of the hydraulic communication between thesecond hydraulic chamber 39 the diversion line 21. Because the pressurelevel in the differential pressure chamber 6 and the work chamber 5 isthe same, the pressure booster 3 is deactivated. Upon triggering of theswitching valve 30, a pressure relief of the control chamber 36 of theservo valve 24 is effected, causing the servo valve piston 32, 65 toopen. Because of the opening force engaging the hydraulic face 44 viathe first hydraulic chamber 38, an exact opening of the servo valvepiston 32 is effected. Upon opening, the first sealing seat 40 is openedfirst, and the slide sealing edge 43 is made to coincide with thecontrol edge 41. The control sleeve 67 is now positioned against thethird housing part 66 by means of hydraulic pressure force in the secondhydraulic chamber 39, and as a result, a high-pressure-proof connectionis achieved. Only after that does opening of the slide seal 69 takeplace, when the servo valve piston portion 65 uncovers the sleeve recess71. As a result, there is no short-circuit leakage flow from the firsthydraulic chamber 38 into the return. The differential pressure chamber6 of the pressure booster 3 now communicates with the low-pressure-sidereturn 28, via the second hydraulic chamber 39, the slide seal 69, thefirst sealing seat 40, and the diversion chamber 42 (low-pressurechamber), and the pressure booster 3 is thus activated.

If conversely the switching valve 30 is closed again, then the servovalve piston 32, 65 moves into its outset position because of thehydraulic pressure force in the control chamber 36 that is operative inthe closing direction. By means of the hydraulic closing force, anexactly defined closing motion is assured over the entire region of theservo valve piston 32, 65. In addition, to reinforce the closing motion,a spring force may be provided. Upon closure of the servo valve piston32, 65, a closure of the slide seal 69 occurs first. As a result, thedifferential pressure chamber 6 of the pressure booster 3 is decoupledfrom the low-pressure-side return 28. Only after a further closingstroke and hence after a delay t₁ does an opening of the control edges41, 43 take place, so that the pressure booster 3 is fully deactivated.Next, the first sealing seat 40 is closed.

Because of the delay t₁ between the closure of the slide seal 69 and theopening of the control edges 41 and the slide sealing edge 43, apressure cushion is still maintained at the injection valve member 14for a short time after the main injection, and this pressure cushion canbe utilized for a postinjection at high pressure. Given this switchingsequence, an overlap of the opening cross sections at the slide seal 69and the control edges 41, 43 is avoided.

From FIG. 4, a variant embodiment with an elongated servo valve pistoncan be seen. Unlike the above-described variant embodiment shown in FIG.3 for a fuel injector 18 which is triggered via a servo valve 24, herethe servo valve piston 32 has a piston portion 65 that is embodied inelongated form. In this variant embodiment, two recesses 70 are embodiedon the end of the servo valve piston portion 65 pointing toward thediversion chamber 42 (low-pressure chamber). Two or more recesses 70 maybe embodied on the circumference of the servo valve piston portion 65.In this variant embodiment, the slide seal 69 is integrated directlywith the first housing part 26 of the servo valve housing 25. In thisvariant embodiment, the control sleeve 67 shown in FIG. 3 on the servovalve piston portion 65 can be omitted.

The mode of operation of the variant embodiment shown in FIG. 4 isidentical to the mode of operation described for the variant embodimentof the fuel injector 18 in FIG. 3.

As shown in FIG. 4, a flat seat is embodied on the end face of the servovalve piston portion 65 that points toward the diversion chamber 42(low-pressure chamber).

In the variant embodiments shown in FIGS. 1 through 4, with a firstsealing seat 40 in the servo valve housing 25, the servo valve 24 mayalso be embodied as a pure slide-slide valve. Care must be taken toassure a sufficient congruent length at the slide seal 69, to keep theleakage flow in the state of repose of the fuel injector 18 small.Besides the mode of operation described above in the form of a 3/2-wayvalve, the servo valve 24 may also be embodied as a 4/2-way valve, inwhich the function of the check valve can be integrated with the slidevalve.

LIST OF REFERENCE NUMERALS

-   1 Pressure source-   2 High-pressure supply line-   3 Pressure booster-   4 Booster piston-   5 Work chamber-   6 Differential pressure chamber-   7 Support disk-   8 Restoring spring-   9 Compression chamber-   10 Overflow line-   11 First throttle restriction-   12 Control chamber for injection valve member-   13 Spring-   14 Injection valve member-   15 Second throttle restriction-   16 Pressure chamber-   17 Pressure chamber inlet-   18 Fuel injector-   19 Injector body-   20 End face of pressure booster piston 4-   21 Diversion line-   22 Injection opening-   23 Combustion chamber-   24 Servo valve-   25 Servo valve housing-   26 First housing part-   27 Second housing part-   28 Low-pressure-side return-   29 Supply line of servo valve-   30 Switching valve-   31 Further low-pressure-side return-   32 Servo valve piston-   33 Through conduit-   34 Third throttle restriction-   35 Control face of servo valve piston-   36 Control chamber of servo valve-   37 Outlet throttle (fourth throttle restriction)-   38 First hydraulic chamber-   39 Second hydraulic chamber-   40 First sealing seat-   41 Control edge-   42 Diversion chamber (low-pressure chamber-   43 Slide sealing edge-   44 Opening face-   50 Refill valve-   51 Damping piston-   52 Fifth throttle restriction-   53 Conduit-   54 Spring element-   55 Annular face-   56 Filling line-   57 First supply line portion-   58 Second supply line portion-   60 Injector switching valve-   61 Injector return-   62 Control chamber sleeve-   63 First recesses-   64 Inlet faces (polished section)-   65 servo valve piston portion-   66 Third housing part-   67 Control sleeve-   68 Control sleeve spring-   69 Slide seal-   70 Second recesses-   71 Control sleeve recess

1-17. (canceled)
 18. A fuel injector for injecting fuel into acombustion chamber (23) of an internal combustion engine the injectorcomprising a pressure booster (3) having a booster piston (4) whichseparates a work chamber (5), permanently subjected to fuel via apressure source (1, 2), from a pressure-relievable differential pressurechamber (6), and a servo valve (24) actuatable to effect a change inpressure in the differential pressure chamber (6), the servo valveopening or closing a hydraulic connection (21, 39, 42) of thedifferential pressure chamber (6) to a low-pressure-side return (28),the servo valve (24) having a servo valve piston (32, 65), which isguided between a control chamber (36) and a first hydraulic chamber (38)and on which an operative hydraulic face (44), constantly urged in theopening direction of the servo valve piston (32) by a system pressure,and a first sealing seat (40), which seals off the servo valve (24) froma low-pressure-side return (28), are embodied.
 19. The fuel injectoraccording to claim 18, wherein the control chamber (36) and the firsthydraulic chamber (38) are subjected to system pressure via a supplyline (29) that originates at the pressure source (1).
 20. The fuelinjector according to claim 19, wherein the control chamber (36) of theservo valve (24) is subjected to system pressure, via a through conduit(33) extending through the servo valve piston (32), from the firsthydraulic chamber (38) into which the supply line (29) discharges. 21.The fuel injector according to claim 20, wherein the through conduit(33) of the servo valve piston (32) includes an integrated throttlerestriction (34).
 22. The fuel injector according to claim 19, whereinthe control chamber (36), via a second supply line portion (57)branching off from the supply line (29), and the first hydraulic chamber(38), via a supply line portion (58) branching off from the supply line(29), are subjected in parallel to system pressure.
 23. The fuelinjector according to claim 22, wherein the first supply line portion(57) comprises a first throttle restriction (34).
 24. The fuel injectoraccording to claim 18, wherein the servo valve piston (32) comprises afirst sealing seat (40), which opens or closes the low-pressure-sidereturn (28), and a control edge (41), which separates the firsthydraulic chamber (38) from a second hydraulic chamber (39).
 25. Thefuel injector according to claim 24, wherein the first sealing seat (40)is embodied as a flat seat or a conical seat and closes an outletcontrol chamber (42) located on the low-pressure side.
 26. The fuelinjector according to claim 24, wherein the control edge (41) isembodied as a slide sealing edge (43).
 27. The fuel injector accordingto claim 18, wherein the differential pressure chamber (6), which can bepressure-relieved into the low-pressure-side return (28) via the servovalve (24), is hydraulically coupled with a control chamber (12) for aninjection valve member (14), which control chamber receives a dampingpiston (51), and the damping piston (51) includes a throttle restriction(52) which defines the opening speed of the injection valve member, andthe control chamber (12) for actuating the injection valve member (14)communicates via a filling line (56) with either the control chamber(12) or one of the hydraulic chambers (5, 6, 9) of the pressure booster(3).
 28. The fuel injector according to claim 18, wherein the actuationof the servo valve (24) is effected via a switching valve (30) thatconnects the control chamber (36) to a return (31).
 29. The fuelinjector according to claim 18, wherein the servo valve piston (32)comprises a reduced-diameter servo valve piston portion (65), and aprestressed control sleeve (67) received on the reduced diameter servopiston portion.
 30. The fuel injector according to claim 29, wherein thecontrol sleeve (67) together with the servo valve piston portion (65)forms a slide control edge (69).
 31. The fuel injector according toclaim 30, wherein the slide control edge (69) controls the communicationwith the low-pressure-side return (28).
 32. The fuel injector accordingto claim 29, wherein the servo valve piston portion (65) of the servovalve piston (32) has first recesses (63), each of which includes aslide sealing edge (43) which cooperates with a control edge (41)embodied toward the servo valve housing.
 33. The fuel injector accordingto claim 29, further comprising a spring element (68) acting on thecontrol sleeve (67), the spring element (68) being braced against ahousing part (26) of the servo valve housing (25).
 34. The fuel injectoraccording to claim 29, wherein the servo valve piston portion (65) ofthe servo valve piston (32) comprises first recesses (63) between thefirst hydraulic chamber (38) and the second hydraulic chamber (39) andsecond recesses (70), the first recesses (63) and second recesses (70)being a slide seal (69).